726 research outputs found
Tunable-filter imaging of quasar fields at z ~ 1. II. The star-forming galaxy environments of radio-loud quasars
We have scanned the fields of six radio-loud quasars using the Taurus Tunable
Filter to detect redshifted [OII] 3727 line-emitting galaxies at redshifts 0.8
< z < 1.3. Forty-seven new emission-line galaxy (ELG) candidates are found.
This number corresponds to an average space density about 100 times that found
locally and, at L([OII]) < 10^{42} erg s^{-1} cm^{-2}, is 2 - 5 times greater
than the field ELG density at similar redshifts, implying that radio-loud
quasars inhabit sites of above-average star formation activity. The implied
star-formation rates are consistent with surveys of field galaxies at z ~ 1.
However, the variation in candidate density between fields is large and
indicative of a range of environments, from the field to rich clusters. The ELG
candidates also cluster -- both spatially and in terms of velocity -- about the
radio sources. In fields known to contain rich galaxy clusters, the ELGs lie at
the edges and outside the concentrated cores of red, evolved galaxies,
consistent with the morphology-density relation seen in low-redshift clusters.
This work, combined with other studies, suggests that the ELG environments of
powerful AGN look very much the same from moderate to high redshifts, i.e. 0.8
< z < 4.Comment: 18 pages, 18 figures, uses emulateapj.cls. Accepted for publication
in A
Tunable-filter imaging of quasar fields at z~1. I. A cluster around MRC B0450-221
Using a combination of multicolour broad- and narrow-band imaging techniques
and follow-up spectroscopy, we have detected an overdensity of galaxies in the
field of quasar MRC B0450-221, whose properties are consistent with a cluster
at the quasar redshift z=0.9. An excess of red galaxies (V-I>2.2, I-K'>3.8) is
evident within 1' of the quasar, with the colours expected for galaxies at
z=0.9 that have evolved passively for 3 Gyr or more. A number of line-emitting
galaxies (nine candidates with equivalent widths EW>70A) are also detected in
the field using the TAURUS Tunable Filter (TTF). Three have been confirmed
spectroscopically to indeed lie at z=0.9. The TTF candidates with the strongest
[O II] line emission cluster in a group which lies 200-700 kpc away from the
quasar and the red galaxy excess, and therefore most likely on the outskirts of
the cluster. These observations are the first in a series probing quasar
environments at z~1 with TTF.Comment: Accepted for publication in AJ. 25 pages, 24 figs (large files in jpg
or gif format), uses emulateapj.st
Anharmonic mixing in a magnetic trap
We have experimentally observed re-equilibration of a magnetically trapped
cloud of metastable neon atoms after it was put in a non-equilibrium state.
Using numerical simulations we show that anharmonic mixing, equilibration due
to the collisionless dynamics of atoms in a magnetic trap, is the dominant
process in this equilibration. We determine the dependence of its time on trap
parameters and atom temperature. Furthermore we observe in the simulations a
resonant energy exchange between the radial and axial trap dimensions at a
ratio of trap frequencies \omega_r / \omega_z = 3/2. This resonance is
explained by a simple oscillator model.Comment: 9 pages, 6 figure
Nonvanishing Energy Scales at the Quantum Critical Point of CeCoIn5
Heat and charge transport were used to probe the magnetic field-tuned quantum
critical point in the heavy-fermion metal CeCoIn. A comparison of
electrical and thermal resistivities reveals three characteristic energy
scales. A Fermi-liquid regime is observed below , with both transport
coefficients diverging in parallel and as , the
critical field. The characteristic temperature of antiferromagnetic spin
fluctuations, , is tuned to a minimum but {\it finite} value at ,
which coincides with the end of the -linear regime in the electrical
resistivity. A third temperature scale, , signals the formation of
quasiparticles, as fermions of charge obeying the Wiedemann-Franz law.
Unlike , it remains finite at , so that the integrity of
quasiparticles is preserved, even though the standard signature of Fermi-liquid
theory fails.Comment: 4 pages, 4 figures (published version
Imaging Fabry-Perot Spectroscopy of NGC 5775: Kinematics of the Diffuse Ionized Gas Halo
We present imaging Fabry-Perot observations of Halpha emission in the nearly
edge-on spiral galaxy NGC 5775. We have derived a rotation curve and a radial
density profile along the major axis by examining position-velocity (PV)
diagrams from the Fabry-Perot data cube as well as a CO 2-1 data cube from the
literature. PV diagrams constructed parallel to the major axis are used to
examine changes in azimuthal velocity as a function of height above the
midplane. The results of this analysis reveal the presence of a vertical
gradient in azimuthal velocity. The magnitude of this gradient is approximately
1 km/s/arcsec, or about 8 km/s/kpc, though a higher value of the gradient may
be appropriate in localized regions of the halo. The evidence for an azimuthal
velocity gradient is much stronger for the approaching half of the galaxy,
although earlier slit spectra are consistent with a gradient on both sides.
There is evidence for an outward radial redistribution of gas in the halo. The
form of the rotation curve may also change with height, but this is not
certain. We compare these results with those of an entirely ballistic model of
a disk-halo flow. The model predicts a vertical gradient in azimuthal velocity
which is shallower than the observed gradient, indicating that an additional
mechanism is required to further slow the rotation speeds in the halo.Comment: 18 pages, 18 figures. Uses emulateapj.cls. Accepted for publication
in Ap
Heat Transport as a Probe of Electron Scattering by Spin Fluctuations: the Case of Antiferromagnetic CeRhIn5
Heat and charge conduction were measured in the heavy-fermion metal CeRhIn5,
an antiferromagnet with T_N=3.8 K. The thermal resistivity is found to be
proportional to the magnetic entropy, revealing that spin fluctuations are as
effective in scattering electrons as they are in disordering local moments. The
electrical resistivity, governed by a q^2 weighting of fluctuations, increases
monotonically with temperature. In contrast, the difference between thermal and
electrical resistivities, characterized by an omega^2 weighting, peaks sharply
at T_N and eventually goes to zero at a temperature T^* ~ 8 K. T^* thus emerges
as a measure of the characteristic energy of magnetic fluctuations.Comment: 4 pages, 4 figure
Nineteen-port photonic lantern with multimode delivery fiber
We demonstrate efficient multimode (MM) to single-mode (SM) conversion in a 19-port photonic lantern with a 50 μm core MM delivery fiber. The photonic lantern can be used within the field of astrophotonics for coupling MM starlight to an ensemble of SM fibers in order to perform fiber-Bragg-grating-based spectral filtering. An MM delivery fiber spliced to the photonic lantern offers the advantage that the delivery fiber guides the light from the focal plane of the telescope to the splitter. Therefore, it is no longer necessary to have the splitter mounted directly in the focal plane of the telescope. The coupling loss from a 50 μm core MM fiber to an ensemble of 19 SM fibers and back to a 50 μm core MM fiber is below 1.1 dB.3 page(s
Field-Induced Quantum Critical Point in CeCoIn5
The resistivity of the heavy-fermion superconductor CeCoIn5 was measured as a
function of temperature, down to 25 mK and in magnetic fields of up to 16 T
applied perpendicular to the basal plane. With increasing field, we observe a
suppression of the non-Fermi liquid behavior, rho ~ T, and the development of a
Fermi liquid state, with its characteristic rho = rho_0 + AT^2 dependence. The
field dependence of the T^2 coefficient shows critical behavior with an
exponent of 1.37. This is evidence for a field-induced quantum critical point
(QCP), occuring at a critical field which coincides, within experimental
accuracy, with the superconducting critical field H_c2. We discuss the relation
of this field-tuned QCP to a change in the magnetic state, seen as a change in
magnetoresistance from positive to negative, at a crossover line that has a
common border with the superconducting region below ~ 1 K.Comment: 4 pages, 3 figures (published version
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